The invention relates to an apparatus for controlling alkaline developing solution used in developing photosensitive organic resin (photoresist, hereinafter called simply resin) in liquid crystal board manufacturing process, printed board manufacturing process or the like, and more particularly to an apparatus combining a continuous automatic replenishing mechanism in cyclic use of alkaline developing solution, an alkali concentration regulating mechanism, and a developing solution automatic discharge mechanism for arresting deterioration of developing performance due to enrichment of dissolved resin.
In liquid crystal board manufacturing process or printed board manufacturing process, an alkaline aqueous solution, such as tetramethyl ammonium hydroxide (TMAH) aqueous solution (for example, 2.380 wt. %) and potassium hydroxide aqueous solution, is used as a developing solution of resin in spray method or dip method.
In the conventional method, starting by filling a development processing tank with the specified volume of a fresh developing solution at the specified concentration, when the developing solution is consumed and reaches a specified deterioration concentration region, on the basis of an empirical index such as the number of boards processed, the whole volume is exchanged with a prepared fresh solution in the batch operation system. This solution exchanging frequency varies with the type of the boards, but it is generally done once in every about six hours.
An alkaline aqueous solution used as the developing solution of resin gradually lowers in the alkali concentration in the course of use due to reaction with acid in the resin, and absorption and reaction of carbon dioxide and oxygen gas in the air, and the effective sensitivity declines sequentially, but, hitherto, the alkali concentration was not measured in real time and controlled at the specified concentration.
Besides, the resin dissolved in the developing solution in the development processing is gradually enriched, and in the positive resist, it functions to slightly dissolve the resin in the unexposed area that should not be dissolved, and the residual film rate of the unexposed part is gradually lowered, but conventionally the resin concentration was not measured in real time and controlled at the specified concentration.
Therefore, in this period, the alkali concentration and the dissolved resin concentration vary with the passing of the time and are not constant, and it was hence difficult to control the delicate dimensional precision in developing the boards, the product quality was unstable, and the yield was lowered.
Besides, due to stopping of operation (down time) for exchanging solution, the operation rate was significantly lowered, and the exchange work of the developing solution required an extra labor cost.
Moreover, since the developing solution was adjusted to the specified concentration and the specified quality, and shipped in an enclosed container free from contamination with foreign matter, the transportation cost was enormous, and as compared with the undiluted developing solution, the material cost was much higher.